Add Cargo.lock to gitignore

[nicoburns]

We don't have Cargo.lock committed, so we should ignore it. Currently it keeps showing up as an untracked file which makes it hard to avoid accidentally committing it as part of unrelated changes. .gitignore is currently not upstream but is part of the "Initial downstream commit".

[Loirooriol]

Shouldn't we commit Cargo.lock instead?

[mrobinson]

Cargo.lock used to be committed, but it increased the size of our diff from upstream. Ultimately, Stylo is used in Servo which has its own Cargo.lock file. As long as thing keep compiling here and in Servo, I think we do not have to commit Cargo.lock. It's a bit unusual for crates to check in their Cargo.lock file in any case.

[nicoburns]

It's a bit unusual for crates to check in their Cargo.lock file in any case.

I believe there was recently a change of advice from the Rust/Cargo teams about this. They previously recommended that libraries don't check in Cargo.toml, and they now weakly recommend doing so. But I think it's pretty much a toss up in terms of advantages/disadvantages, and many crates still don't. As it's a bit of a pain for Stylo I suggest we just don't for now (we can always commit it again later, but I would personally consider that low priority).

[mrobinson]

I think this is okay for now.